The term paramedian raphe nucleus refers to a narrow layer of cells located lateral to the median raphe nucleus in the pontine reticular formation. It is found in the human ( Hornung-2012 ), the macaque ( Paxinos-2009a ), the rat, Swanson-2004 ), and the mouse ( Franklin-2008 ). In the primate, but not the rodent, it contains a significant number of serotonin containing cells: B8 cell group dorsally; B9 cell group ventrally ( Felten-1983; Hornung-2012 ). Functionally it is part of the behavioral state system, known there as the superior central nucleus raphe, lateral part ( Swanson-2004 ).